This invention relates to an apparatus for clamping flexible tubes, as is set forth in the preamble of the main claim and known from German patent specification 33 44 849 A1.
In the technical medical field, in particular in the case of extracorporeal circulations, it is often necessary to open or shut flexible tubes by means of clamps in a specific way. A typical example thereof is the dialysis with extracorporeal circulation using a single needle arrangement. During one operating cycle the flexible tube portions of the arterial and venous legs must respectively be opened or closed. This is carried out via corresponding clamps.
The clamping devices known from the prior art make use of lifting or rotary magnets which are operatively connected to a corresponding mechanism. These magnets have the great disadvantage that they consume a very great amount of power and lead to a considerable heat emission in the operative state. Another disadvantage of the magnets is the enormous noise which may disturb or affect patients, especially during dialyses that last for several hours.
German patent specification 33 44 849 A1 shows a safety means for infusion control devices wherein a flexible tube can be clamped by means of a sword which is displaceably supported in a direction transverse to the flexible tube. The sword is operated via a cam which is arranged on an output shaft of a gear system. The device serves as a safety means which is to have the particular effect that the infusion operation is interrupted in case of power failure. It follows therefrom that the device is not suited for continuously opening or closing a flexible tube during the infusion operation because the gear system itself as well as the stepping motor exhibit great inertia and cannot be designed without play in such a way that the valve function to be exerted by the sword is ensured in a reliable and quickly responding way.
German patent specification 31 04 985 A1 discloses a conveying or pumping apparatus wherein a flexible tube can be selectively clamped by means of two clamping elements, while a pump plunger with the aid of which the liquid volume between the two clamping elements can be displaced into the flexible tube is arranged in the area between the two clamping elements. With this apparatus a driving operation is carried out through a cam shaft which is provided with cams that are in operative communication with the pump element and the clamping elements respectively. This apparatus is not suited for exactly and reliably clamping a flexible tube of an infusion means because the clamping means are only intended for the pumping or conveying operation.
German patent application 15 41 363 discloses an infusion means in the case of which the flexible tube is clamped by means of a solenoid. As a consequence, this means has the disadvantages already mentioned in the introduction to the specification.